The issue visible on second page, the black line on the right caused by reduction of image resolution, has already been fixed in 1.4.5svn. See issue 0012294.

As for the issue visible on first page, I'm not sure what we can do about it, and if we can do anything :
- it appears in areas where imported image is only partially transparent. Those areas are thin but easily detectable in Photoshop.
- Adobe Photoshop does not show those line when rendering exported PDF.
- in latest Acrobat Reader, the visibility of those lines depends essentially on zoom factor.
So this looks more like a rendering artefact. In any case Scribus canvas shows correctly there might be some issue as those lines can be seen directly on canvas.